Iron strip is actually composed of lead.
I wouldn't be surprised if they used some sort of insecticide because if you're into aquatic plants, leaf miner caterpillars are the some of the worst pests/hitchhikers to introduce into your planted invert tank.
These mining leaf cutting pests are an absolute menace once they get a breeding colony in your tank. Those things can strip all the leaves your tank in a few weeks if you don't pay attention.
A lot of places that do sell plants don't think much about inverts unless it's something they specialize in. It's helpful to actually know the people who maintain their aquatics section, so you can find out what they treat their items with.
Unfortunately you almost always have to be suspicious of everything that gets placed inside their environment.
This is why everyone has different types of qt methods & chemicals to dip their plants/decorations in.
Good luck with the amanos you have in treatment.